Here is a list of GSM Carriers/Service Providers in the USA.

Airfire Mobile
ASTAC
Asset/Vada Wireless
AT&T (Includes GoPhone Prepaid, Dobson Cellular, Edge Wireless and Centennial Wireless)
Broadpoint
Big Sky Mobile
Calhan Wireless
Call4care
Cellular One of East Central Illinois
Cellular One of East Arizona

Cellular One Nation
Cellular One TXOK
Chariton Valley Wireless
Cincinnati Bell Wireless
Commnet Wireless (also uses CDMA in some areas)
Consumer Cellular
Cordova Wireless
Corr Wireless

Cricket Wireless
Cross Communications
DTC Wireless
Earthtones
Epic PCS
FreedomPop
Fuzion Mobile
GCI Wireless (also uses CDMA in some areas)
GTC Wireless
GoSmart Mobile

i wireless
Immix
Indigo Wireless
Jolt Wireless
KTC PACE
Long Lines Wireless
Mobal Freedom
Metro PCS (also uses CDMA in some areas)

NEP Wireless
Pine Cellular
Plateau Wireless
Pure Prepaid
Pure Talk USA
Simple Mobile
Telecom North America Mobile Inc
TerreStar
T-Mobile USA

TracFone Wireless (also uses CDMA in some areas) (Includes NET10 Wireless, SafeLink Wireless, Straight Talk, SIMPLE Mobile and Telcel América)
Tru
Union Wireless
Viaero Wireless
Wal-Mart Family Mobile
West Central Wireless
Westlink
XIT Communications

The accuracy of this list is not guaranteed. There are new carriers, and carriers closing down, plus changes to carrier info constantly, so to be sure ask your provider to be sure.

Looking for other helpful how-to tutorials? Click here for a full list of all my tutorials.